Backgound: Most functions that take an iterable as parameter iterate just once. Users of the function can pass any iterable, including iterators. The function will call iter(imput) and go. If the user wants to iterate thru a virtual collection defined by an instance of an iterator class (built-in or user-defined) or generator function, the user must call the gf/ic with the appropriate arguments and pass the result. Problem: Some functions iterate thru the input more than once. If the input is not an iterator, there is no problem: call iter(input) again. If the input is an iterator, that just returns the now-empty iterator. Bad. General solution: The most general solution is for the caller to pass the result of list(it) instead of it. If the caller starts with only an iterator, that is the only solution I know of. Special solution: If the caller starts with an non-iterable iterator source -- iterator class or generator function (which can be regarded as defining a virtual subclass of iterator class 'generator') -- it might be better to package that source and required args as an iterable. class gfic: #untested as yet def __init__(self, func, *args, **kwds): self.func = func self.args = args self.kwds = kwds self.__name__ = func.__name__ def __iter__(self): return self.func(*self.args, **self.kwds) This is similar, I believe, to functools.partial except that the wrapping is total rather than partial and the wrapped call is in __iter__ instead of __call__. Would this be a sensible addition to functools, say, or is the use case too rare? Terry Jan Reedy